In a conventional surgical operation, the surgeon operates on an organ using his visual and tactile senses in order to locate his hand and the surgical tool in the correct position. In Computer Assisted Surgery (CAS) however, the motion of the surgical tool is generally determined by a pre-operative plan, with the actual operating location being pre-planned using pre-operative X-ray, CT, MRI or other images. During the operation, it is necessary to transfer this planning information to the operation site, generally by mutually referencing the coordinate system of the patient, the position of the surgical tool and the data provided by the pre-operative plan. This is known as a registration procedure.
It is therefore important to provide the computer with accurate information concerning the patient position relative to the navigation/robotic system. This is accomplished in contemporary CAS devices by either holding the body part on which the operation is being performed, in a fixed position following the registration process, or by attaching a dynamic referencing device which moves with the body part being operated on, and compensates for undesired motion by means of dedicated tracking software.
In spinal operation CAS procedures, if the procedure is to be performed on more than one vertebra, it is necessary, according to prior art methods, to affix dynamic referencing sensors at each level of the spine, or even on each vertebra, so that relative motion between different regions of the spine or even between different vertebrae can be detected and compensated for. Alternatively, all of the vertebra to be operated on are fixed to a stationary frame to ensure well-defined positions. Both of these alternatives are complex and inconvenient procedures.
There therefore exists an important need to provide a method of enabling CAS to be performed on several vertebrae in a single procedure, by means of a simple apparatus.
Additionally, when surgery is to be performed to correct or treat conditions related to spinal curvature, according to prior art methods the surgeon has generally used visual means for estimating the position of the vertebrae at different levels of the back. Such visual estimation, whether based on manual manipulation of the operating tools, or CAS guidance thereof, is potentially inaccurate and highly dependent on the surgeon's skill. There therefore also exists a need to provide a reference method for providing the surgeon with information about the relative location of vertebrae over the whole length of the spine.